Biotechnological advances are leading to new peptide/protein drugs of great promise for human health. Unfortunately, oral administration usually is ineffective in delivering such drugs, which must be taken parenterally. Recently, transpulmonary drug delivery has shown considerable potential as an alternative route of systemic delivery. Therefore, in this proposal, our long term goals are to elucidate the mechanisms for absorption of peptide and protein drugs across the alveolar epithelium, the surface across which drug absorption from lung airspaces must occur. Although pulmonary delivery of protein/peptide drugs has been shown in animal studies to lead to promising bioavailabilities, absorption mechanisms and pathways are virtually unknown. Bioengineering related issues pertaining to pulmonary drug delivery include formulation modalities, delivery approaches and transepithelial transport. Of these, we chose to delineate specific mechanisms that may prevail in absorption of peptide / protein drugs across alveolar epithelium. We will utilize primary cultured rat alveolar epithelial cell monolayers as an in vitro model and use di-/tri-peptides, granulocyte-colony stimulating factor and human growth hormone as model drugs. We propose to i) delineate the mechanisms and pathways (i.e., paracellular diffusion, fluid-phase transcytosis, receptor-mediated and/or adsorptive transcytosis) for absorption of model protein drugs across the alveolar epithelial barrier, ii) investigate the mechanisms underlying stimulation of protein drug absorption via transcytosis across the alveolar epithelial barrier, iii) investigate how peptide drugs are absorbed across the alveolar epithelium, and iv) determine the stimulatory effect of physicochemical variables on alveolar epithelial absorption of protein/peptide drugs. Through the collaborative investigation of pulmonary protein/peptide drug absorption among four different biomedical research laboratories utilizing experimental approaches spanning cell biology to bio(chemical)engineering, results from these projects will provide new information for advancing bioengineering approaches to pulmonary drug delivery, including development of new methodologies to improve bioavailability via the alveolar epithelial barrier.